In some ways, these presidential ticket No. 2s could not be more different. They are separated in age by nearly three decades, were born to families in different regions of the country and have views on opposite ends of the political spectrum.

But in other ways, the 42-year-old Republican congressman and 69-year-old Democratic vice president are very much alike. Both were born to Catholic families in working-class neighborhoods and were young stars in their parties who became experts on the inner workings of Washington.

And perhaps above all, these men both do political things their respective No. 1s cannot.

Biden, with his back-slapping image, big smile and hardscrabble roots in Scranton, Pa., is seen as more effective than President Barack Obama at courting white working-class voters. Ryan, while less known outside his Janesville, Wis., hometown, is a favorite of the Republican Party's conservative base, a group that long has been skeptical of Republican presidential contender Mitt Romney's conservative credentials.

Over the next three months, Biden and Ryan will play key roles in the White House race, raising money, criticizing the opponent and helping lend credibility in complicated policy debates - Biden on foreign policy and Ryan on federal budgeting. They will also inevitably create headaches for their bosses, as Biden did this week when he told a Virginia crowd that included hundreds of black people that Romney's plans for Wall Street would put them "back in chains."

Mostly, their job: Sell the boss to Americans - and tear down the other guy.

Routinely, Biden says Obama has "a backbone like a ramrod" and says he considers himself Obama's older brother. He also unleashes scathing attacks against Romney and, now, Ryan, including his proposals to overhaul Medicare.

Ryan, just days into his new role, has said repeatedly of Romney that he's "the kind of man who you want to serve as your president. He's the kind of man who, when he gets involved, he fixes things." And he lambasts Obama, saying he's "spending our children into a diminished future."

When talking to voters, both often offer personal touches.

While visiting a firehouse in Hillsborough, N.C., to thank firemen for the work they do, Biden shared the story of his first wife's and daughter's deaths in a car accident. Then, at high school football practice in Danville, Va., he offered some of his father's favorite words: "When you get knocked down, get up!"

With a football in his hand, the silver-haired Biden told players that when he played high school football he weighed about 158 pounds but with pads he clocked in at 175. Asked if he was ready to suit up and play, the vice president declared, "I'm ready to go!"

It was a moment of connection for a man who has maintained his everyman appeal, despite having worked nearly 40 years in Washington. Elected to the Senate at 30, he commuted by train more than two hours most days to and from Delaware to see his family. An Amtrak station in Wilmington, Del., was named in his honor last year.

Biden's kids have long since grown up. Two of them are about the same age as Ryan. But he often refers to his grandchildren on the campaign trail, including one story that he uses to accuse Republicans of creating the country's economic mess: "As my youngest granddaughter, Natalie, says, 'Who do they think did that, Casper the ghost?'"

Ryan became a congressman at just 28 and is nearing the end of his seventh term. He's been sharing stories about camping, his exercise routine and demolition derby as he has crisscrossed six states - Virginia, Wisconsin, Iowa, Colorado, Nevada and Ohio - on Romney's behalf this week.

He chatted about cow milking during a brief tour of the Iowa State Fair on Monday. The next day, his young children - and love for the outdoors - figured prominently in a speech in Colorado, where he took his family camping last summer.

Ryan said he showed his kids - Liza, 10, and sons Charles, 8, and Sam, 7 - how to cook a meal on a campfire and make s'mores. Later, he and his wife, Janna, put the kids to bed in a tent.

"We stayed up late and we talked about our country," Ryan said. "There's nothing like the stars and the skies of the Colorado Rockies at night. We looked at our kids and we know they are our future. But today, we look at our kids and we know, without a shadow of a doubt, that we are mortgaging their future."

When he makes comments like these, Ryan exudes a certain cheery authenticity. He is a former personal trainer, a skier and hiker known for his devotion to the workout routine known as P90X. The Republican chairman of the House Budget Committee, Ryan is someone who draws budget graphs on napkins. He defends complicated Medicare plans with a boyish charm that prompted New York Times liberal columnist Maureen Dowd to call him "the cutest package that cruelty ever came in."

"Ryan strikes me as a policy wonk who's not a nerd," said Steve Duprey, a member of the Republican National Committee from New Hampshire.

Where Ryan's forte is the budget, Biden is an expert on foreign policy, having served as the chairman of the Senate Foreign Relations committee. Neither Romney nor Ryan has significant foreign policy experience.

Biden has significant credibility in the foreign policy realm, despite a tendency to stray off message.

His use of profanity was betrayed when television cameras captured him mouthing a colorful congratulations to Obama after the passage of his health care law. And just this week, he told a Virginia crowd that Obama needed their help to win North Carolina and referred to the country being in the 20th century - when it's the 21st century.

Biden made a more significant misstep while criticizing Romney's plans to eliminate new Wall Street regulations. "Unchain Wall Street," Biden told a crowd that included hundreds of blacks. "They're going to put y'all back in chains." Romney seized on the comments as proof Obama's campaign is driven by "division and attack and hatred."

Former Rep. Tom Perriello, D-Va., who introduced Biden at a rally this week, said the vice presidential campaign was a study in contrasts. Biden may be a generation older than Ryan, he said, but the vice president "hasn't missed a step."

"He may not work out as aggressively as Paul Ryan, but both of them are plenty fit," Perriello said.

Introducing Ryan this week, former Colorado Rep. Bob Beauprez said that there's one important thing to remember about Ryan: "He ain't Joe Biden."